Choosing between OS2 and OM3 fiber is the single most common decision in fiber cabling — and it is decided by your transceivers, not by the cable. Here is the honest, no-marketing version.
The one-line answer
OS2 is single-mode fiber for long links. OM3 is multimode fiber for short, fast links. If your optics say “LR” (long reach), you need single-mode. If they say “SR” (short reach), you need multimode. The cable must match the optics — they are not interchangeable.
Side by side
| OS2 Single-Mode | OM3 Multimode | |
| Core | 9/125μm | 50/125μm |
| Wavelength | 1310 / 1550 nm | 850 nm |
| Typical optics | SFP+ LR, QSFP LR4, BiDi | SFP+ SR, QSFP+ SR4 |
| 10G reach | ~10 km (with LR optics) | up to 300 m |
| 40G/100G reach | 10 km class (LR4) | 100 m / 70 m |
| Connector color | Blue (UPC) | Aqua (UPC) |
| Best for | Building-to-building, FTTH, outdoor runs, campus backbone | Data center rooms, short equipment interconnects |
Which one should you buy?
- Outdoor runs, buried conduit, between buildings, anything over ~300m: OS2. Our OS2 armored cables use G.657.A2 bend-insensitive single-mode fiber and come in 2-fiber duplex and 4-fiber configurations.
- Inside a data hall, rack-to-rack, short 10G/40G/100G links: OM3. Our OM3 armored duplex cables pair aqua LC Uniboot connectors with a pre-installed pulling eye for conduit pulls.
- Check your transceiver first: the optics datasheet always says which fiber type it expects. Buying cable that matches your optics is the whole game.
Distance figures above are the standard OM3/OS2 ratings from the fiber specifications; cable construction (armored or not) does not change optical reach.